ABSTRACT This proposal lends strong support to the new concept of tight junction associated proteins as key regulators of epithelial homeostasis in the intestine. It is now appreciated that tight junction (TJ) proteins are not static barrier forming units, but act as dynamic signaling centers to fine tune many critical epithelial cellular functions ranging including proliferation, migration and cell survival. Indeed, inflammatory conditions such as ulcerative colitis and crohns disease are associated with a leaky gut, epithelial proliferation and impaired wound healing/mucosal ulceration that is, in part, related to altered expression of tight junction proteins. Pertinent to this project, we have compelling evidence of the importance of TJ associated CTX proteins, junctional adhesion molecule A (JAM-A) and CAR Like Membrane Protein (CLMP), that play complementary roles in the regulation of mucosal homeostasis by promoting epithelial barrier function and downregulating IEC proliferative responses. Intriguingly, we have observed reduced JAM-A in epithelial cell-cell contacts under inflammatory conditions while CLMP expression, in contrast, is enhanced, suggesting coordinated fine tuning of CTX-dependent epithelial responses under conditions of perturbed homeostasis.The goal of this proposal is centered on elucidating fundamental mechanisms of how JAM-A and CLMP regulate crucial epithelial barrier function and cellular proliferation. In Aims 1 and 2, we will extend preliminary findings that identify new signaling elements controlling JAM-A-mediated regulation of barrier and epithelial proliferation, respectively. In aim 3, with new inducible, tissue targeted knockout mice, we will define, for the first time, the role of CLMP in regulation of epithelial barrier function and proliferation. The proposed studies will not only shed new light into mechanisms of outside-in signaling at the TJ that regulate permeability and proliferation, but may also provide new ideas for therapeutic targets with diverse applications ranging from enhanced vaccine/drug delivery to wound healing/anti-inflammation or inhibition of cancer progression.